Dave wrote:
On Fri, 24 Feb 2006 01:39:46 GMT, Gary said:


My experience is different. When free diving you can't equalize because
you don't have an air feed at ambient pressure. (Your last breath was at
the surface) Unless I am not understanding the term "free diving" which
I believe means diving without tanks. I that case the air inside your
body gets compressed as you descend and you can't equalize by taking in
more air.


You are misunderstanding. An ear squeeze is caused, not by the difference in
pressure between surface pressure and inner ear pressure, but by low
pressure in the inner ear (which may or may not equal what the pressure was
at the surface) compared to the pressure being exerted by the water pressing
on ear drum from the outside. Since your Eustachian tubes where they join
the throat are flat like the opening of a balloon, the increased air
pressure in your throat doesn't get passed through to the inner ear,
creating a relative vacuum, so the ear drum gets "sucked in". Equalizing
consists, not of adding air from the surface, but of opening the path from
your inner ear to your throat (where the air is, as you say, compressed), so
the higher pressure air there can get into the inner ear and eliminate the
relative vacuum.
I understand clearly. What I am saying is that you can't equalize your
internal air pressure without breathing air a ambient pressure except at
very shallow depths. You need to take in air at the ambient pressure to
equalize properly.